Field of the Invention
The present invention relates to a screening test method and a screening test apparatus used to detect a low-strength portion in an optical fiber.
Description of Related Art
In a process of manufacturing an optical fiber, in order to ensure the strength of the optical fiber to be shipped as a product, while the optical fiber travels continuously in the final manufacturing stage, a tensile test is continuously conducted by applying tension to the optical fiber to break a low-strength portion and remove the broken optical fiber or the vicinity of the broken portion. This type of continuous tensile test is referred to as a screening test.
As a typical example of the screening test apparatus, for example, there has been known an apparatus shown in FIG. 1.
In a screening test apparatus S shown in FIG. 1, an optical fiber 1 to which a screening test method is applied is continuously fed from a sending side bobbin 3, passes a dancer device 5, and travels continuously while sequentially running along a sending side belt lap type capstan 7, a plurality of turn pulleys 9a to 9e, and a receiving side belt lap type capstan 11. Further, the optical fiber sequentially runs along a first pulley 21 and a second pulley 22 on the receiving side and wound by a winding bobbin 23. Then, for example, a weight 13, as tension applying means, is provided to any turn pulley of the plurality of turn pulleys 9a to 9e between the sending side belt lap type capstan 7 and the receiving side belt lap type capstan 11, for example, to the turn pulley 9d, and predetermined tension is forcibly applied to the optical fiber 1 between the sending side belt lap type capstan 7 and the receiving side belt lap type capstan 11. Accordingly, in the example of FIG. 1, a portion from the sending side belt lap type capstan 7 to the receiving side belt lap type capstan 11 corresponds to a tension applying section 15.
Here, when there is a low-strength portion in the optical fiber 1 which is supplied to a screening test, the low-strength portion of the optical fiber 1 is broken by the tension applied in the tension applying section 15 between the sending side belt lap type capstan 7 and the receiving side belt lap type capstan 11. Accordingly, the optical fiber which is finally wound by the winding bobbin 23 is an optical fiber of which the strength is ensured.
In the optical fiber screening test, when the optical fiber is broken, a phenomenon that a broken terminal portion of the optical fiber (a ruptured end portion) beats the normal optical fiber (an optical fiber on an outer circumference of the winding bobbin) which has already been wound around the winding bobbin 23, that is, a phenomenon referred to as fiber beating, occurs in some cases. When the fiber beating occurs, the optical fiber which has been already wound around the winding bobbin 23 is damaged or the performance is deteriorated, and thus, there is a concern that a defective product may be manufactured.
The fiber beating phenomenon is generally considered as follows.
That is, in the screening test, when the optical fiber is broken on the way, the ruptured end is in a free state in which the end is not restricted by external force. Therefore, when the rotation of the winding bobbin is not stopped before the terminal portion of the ruptured end reaches the winding bobbin, a phenomenon that the terminal portion of the ruptured end of the optical fiber rotates with the rotation of the winding bobbin while moving violently on an outer circumference of the optical fiber which has already been wound around the winding bobbin (this phenomenon is referred to as “co-rotation” below) occurs. The terminal portion of the ruptured end of the optical fiber which is co-rotated while moving violently beats the optical fiber which has been already wound around the winding bobbin 23 in some cases.
In order to prevent the fiber beating from occurring in the optical fiber screening test, when the optical fiber is broken on the way, it has been performed that the rotation of the winding bobbin is stopped by increasing a deceleration rate of a speed reducer in a drive system of the winding bobbin 23, or by applying mechanical or electrical control (braking) to the winding bobbin 23 by detecting the breakage by any breakage detecting means in the related art. However, actually, some time is required from when the optical fiber is broken and the breakage is detected to when the rotation of the winding bobbin 23 is decreased and the rotation of the winding bobbin is actually stopped. Therefore, when the rotation of the winding bobbin is not actually stopped, the ruptured end of the optical fiber reaches the winding bobbin and fiber beating occurs.
Particularly, in recent years, a travelling speed of the optical fiber has increased in the screening test with an increase in a process rate of manufacturing an optical fiber, and the screening test is conducted while the optical fiber continuously travels at several tens of m/sec or higher. Therefore, an impact of the above-described fiber beating is large and thus, there is a very high concern that the optical fiber on the winding bobbin may be damaged when the fiber beating occurs. In addition, when the screening test is conducted while the optical fiber continuously travels at a high speed of several tens of m/sec or higher, the travelling distance of the ruptured end of the optical fiber is significantly increased from the occurrence of the breakage to the actual stop of the rotation of the winding bobbin. Therefore, the rotation of the winding bobbin cannot be stopped in most cases before the ruptured end reaches the winding bobbin, and as a result, the frequency of fiber beating increases.
As the related art which prevents fiber beating from occurring when breakage occurs in the optical fiber screening test, there is disclosed a technique in Japanese Unexamined Patent Application, First Publication No. H10-114537.
In the technique in Japanese Unexamined Patent Application, First Publication No. H10-114537, a length of a travelling path (a pass line) of an optical fiber from a place for breaking a low-strength portion of the optical fiber (a screening wheel) is extended (pass line extending means) to a winding bobbin to control the length of the optical fiber travelling path from the broken place to the winding bobbin to be longer than a winding length of the optical fiber from when the optical fiber is broken to when the optical fiber is wounded around the winding bobbin. In order to realize such control, there is disclosed means, by providing winding amount detecting means used to detect a winding amount of the winding bobbin, used to control braking of the winding bobbin according to the detection at the time of breakage, or the like.
However, even when the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber reaches the winding bobbin by applying the method proposed in Japanese Unexamined Patent Application, First Publication No. H10-114537, actually, it is difficult to reliably prevent fiber beating from occurring. That is, when the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber reaches the winding bobbin, the ruptured terminal portion of the optical fiber, which still remains without being wound around the winding bobbin at the time point at which the rotation of the winding bobbin is stopped, flies linearly toward the winding bobbin at a moment in which the winding bobbin is stopped by the linear inertial force in a travelling direction of the optical fiber until the moment. Therefore, there is a possibility of fiber beating occurring.
In addition, when the method proposed in Japanese Unexamined Patent Application, First Publication No. H10-114537 is actually applied, extension of the pass line is caused, and the size of equipment and the cost of equipment increase. Further, since it is necessary to extend the pass line, it is difficult to apply the method to an existing screening test apparatus.
In contrast, in Japanese Unexamined Patent Application, First Publication No. 2004-59243, there is disclosed a technique used to control the rotation of a winding bobbin to be stopped before a ruptured end of an optical fiber reaches the winding bobbin in the same manner as described above. Further, it is proposed that a fiber beating preventing cover having a gap through which the optical fiber can pass without being in contact with the gap is provided immediately before the winding bobbin, and the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber passes through the preventing cover.
According to the technique proposed in Japanese Unexamined Patent Application, First Publication No. 2004-59243, fiber beating may be prevented by co-rotation with the rotation of the winding bobbin and also, fiber beating caused by the above-described linear inertial force may be prevented to some extent.
However, even according to the technique proposed in Japanese Unexamined Patent Application, First Publication No. 2004-59243, it is difficult to reliably and stably prevent fiber beating. That is, the fiber beating occurring when the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber reaches the winding bobbin is caused not only by the linear inertial force of the optical fiber at the time when the rotation of the winding bobbin is stopped as described above. That is, a phenomenon that, while moving violently, a terminal portion of the ruptured end is wound around an outer circumference of the winding bobbin which has been already stopped by the inertial force in a rotation direction of the winding bobbin, and at this time, the free terminal portion of the ruptured end of the optical fiber beats the already-wound fiber, also causes fiber beating. Particularly, when a travelling speed (line speed) of the optical fiber is high, the above-described phenomenon occurs easily. However, the fiber beating caused by the inertial force in the rotation direction cannot be prevented in the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-59243.
In addition, when the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-59243 is applied to an existing screening test apparatus, it is difficult to add the fiber beating preventing cover.
The present invention has been made in consideration of the above-described circumstances and provides a method capable of reliably and stably preventing fiber beating with a rotation stop of a winding bobbin when a low-strength portion in an optical fiber is broken during a screening test of the optical fiber, and of preventing the fiber beating without extension of a pass line, an increase in the cost of equipment, and difficulty in application to an existing screening test apparatus, and an apparatus used to implement the method.
Herein, the inventors have intensively analyzed and studied a phenomenon that, when an optical fiber is broken in an optical fiber screening test, a terminal portion of a broken place collides with an optical fiber which has been already wound around a winding bobbin, that is, causes of fiber beating, and as a result, it is determined that roughly the following three phenomena cause the fiber beating.
A first phenomenon is that the rotation of the winding bobbin is not stopped before the ruptured end of the optical fiber reaches the winding bobbin, and the terminal portion of the optical fiber beats the already-wound fiber such that while moving violently, the broken free terminal portion rotates with the rotation of the winding bobbin on the outer circumference of the winding bobbin, as described above.
A second phenomenon is that even when the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber reaches the winding bobbin, the terminal portion of the optical fiber on the ruptured side, which remains without being wound around the winding bobbin until the rotation of the winding bobbin is stopped, flies linearly toward the winding bobbin by the linear inertial force, which is caused by travelling toward the winding bobbin until the rotation stop, at the time when the winding bobbin is stopped, and collides with the optical fiber which has been already wound around the winding bobbin.
A third phenomenon is that even when the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber reaches the winding bobbin similar to the above description, while moving violently, the terminal portion of the optical fiber on the ruptured side, which remains without being wound around the winding bobbin until the rotation of the winding bobbin is stopped, is wound around the outer circumference of the winding bobbin which has been already stopped by the inertial force in the rotation direction of the winding bobbin, with the rotation of the winding bobbin until the rotation stop. During the winding, the free terminal portion of the ruptured end of the optical fiber beats the already-wound fiber. When the line speed is high, this phenomenon is significant.
Among the three phenomena, the fiber beating caused by the first phenomenon can be solved by stopping the rotation of the winding bobbin before the ruptured end of the optical fiber reaches the winding bobbin as shown in the above-described Japanese Unexamined Patent Application, First Publication No. H10-114537 and Japanese Unexamined Patent Application, First Publication No. 2004-59243.
On the other hand, both the fiber beating caused by the second phenomenon and the fiber beating caused by the third phenomenon are phenomena that can occur even when the rotation of the winding bobbin is stopped before the ruptured end of the optical fiber reaches the winding bobbin. Accordingly, in the technique disclosed in Japanese Unexamined Patent Application, First Publication No. H10-114537, it is difficult to prevent the fiber beating from occurring. In addition, in the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-59243, the fiber beating caused by the second phenomenon, that is, the fiber beating caused by the linear inertial force of the optical fiber at the time when the rotation of the winding bobbin is stopped can be prevented to some extent by providing the fiber beating preventing cover on an upstream side of the winding bobbin. However, the technique does not always reliably prevent the fiber beating and further, the fiber beating caused by the third phenomenon, that is, the fiber beating caused by the inertial force of the optical fiber in the rotation direction of the winding bobbin at the time when the rotation of the winding bobbin is stopped cannot be prevented.
Accordingly, when the above-described three phenomena can be avoided from occurring simultaneously, it is considered that fiber beating can be reliably and stably prevented.